NASA announcement: Seven new worlds

IS this an intergalactic housing estate? Seven Earth-sized worlds have been found orbiting a single star 39 light-years away. And these new worlds could hold life.

The red dwarf star TRAPPIST-1, which sits in the constellation of Aquarius and barely the size of Jupiter, was thought a year ago to have three planets in orbit around it.

This initial discovery caused scientists to keep a close eye on the star. But now a study published in the science journal Nature has exposed a wealth of worlds which are generally thought of as being rare.

NASA has just made the incredible announcement: Seven Earth-sized exoplanets around the one star. All are thought to be mostly made up of rock and could potentially support liquid water on their surfaces.

Three are close to the star, and may be a little too hot to hold much liquid water.

One - the seventh - may be an ice world.

But three of them fall comfortably in the "habitable zone" - orbits neither too hot nor too cold.

That means they may have strong potential to sustain life as we know it.

"This is really the first time we have seven planets that we can say are in the terrestrial zone, and it's really, really surprising," said study co-author and astronomer at the Université de Liège in Belgium, Michaël Gillon.

Thomas Zurbuchen, associate administrator of the Science Mission Directorate at NASA Headquarters in Washington, said: "The discovery gives us a hint that finding a second Earth is not just a matter of if, but when. Are we alone out there, we are making a leap forward to answering this question."

The takeaway from all this is, "we've made a crucial step toward finding if there is life out there," said the University of Cambridge's Amaury Triaud, one of the researchers.

But co-author Amaury Triaud from the Institute of Astronomy in Cambridge, UK, says it is very hard to know if such an abundance of Earth-like planets is common.

As for hosting life, there are complications.

Professor Gillon and colleagues emphasise that further observations are required to thoroughly detail the nature of these planets - especially the seventh. This outermost planet has not yet had its orbital period defined.

Given TRAPPIST-1 is just 39 light years away, this opens up the opportunity for much more detailed observation of the planets as a new generation of telescopes come online, including the Hubble-replacement space-based telescope, the James Webb Telescope next year.

Another specialist planet-hunter will also be launched in 2018, the Transiting Exoplanet Survey Satellite.

With seven worlds all orbiting so close to one another, they may be 'pulling' on each other in unusual ways.

"It's a very small, very compact system," says ays Emmanual Jehin, a co-author on the study. "The seven planets are all included well inside the orbit of Mercury."

Such gravitaitonal 'squeezing' could heat up the planets' cores.

This is significant.

It could do to the seventh ice world what is happening with moons like Europa and Enceladus: melt water under its ice surface. Again, this brings with it the potential for life.

It could also contribute towards giving the worlds a magnetic field - a protective shield against the red dwarf's solar flares.

"This star is extremely quiet compared to other very small stars. It's very calm compared to Proxima Centauri, for example," Jehin says. "If we're optimistic, at least five of the planets-maybe not the first and maybe not the last-but at least five could have some liquid water on the surface, if they have atmospheres and the right pressures."

Debate continues raging among astrobiologists and astrophysicists as to whether or not planets around small - but active - red dwarf stars can hold an atmosphere long enough for microbial life to take hold.

This is because such worlds need to orbit close to the star for the required warmth, which in turn brings them within the reach of solar flares. Such flares could strip away atmospheres over time, as well as regularly irradiate the planet's surface.

These planets are also likely to be 'tidal locked' - orbiting with one face permanently turned towards the star, and the other in perpetual darkness. The result would be an environment utterly unlike our own.

"It's possible their atmospheres are very similar to the Earth, or Venus, or something completely different," Professor Gillon says.

The discovery of potentially habitable exoplanets around TRAPPIST-1 follows a similar announcement by NASA in July 2015: The discovery of 'Earth's cousin', or Kepler 452b.

This world is exciting as it is just 1.6 times larger than Earth, and in orbit around a yellow star similar to our own Sun.
While very little can be discerned from the 'blip' the planet makes when it passes between us and its star, it is believed it is both rocky and capable of supporting an atmosphere.

Once again, exactly what form the planet takes is almost entirely speculation.

Chances are, Kepler 452b is another Venus.

At six billion years, it's an old world. It is likely to have double our gravity.

But its star is both 20 per cent larger than our own and puts out about 10 per cent more energy.

This means Kepler 452b, which sits on the inner edge of the 'goldilocks zone', is likely to be a bit steamy.

That means a climate cascade towards a greenhouse effect - like Venus - is likely.